Work out percentage discounts instantly! - By tecmath
Transcript
00:0-1 | Welcome to take Math Channel . We're going to be | |
00:02 | having a look at this video is we're going to | |
00:03 | be looking about how to mentally take off a percentage | |
00:07 | . Okay . And the reason for this is because | |
00:09 | quite often you go into a shop , another horror | |
00:11 | story and I'll have something like , You know , | |
00:14 | 25% off this amount or 20% from this amount or | |
00:18 | 50% off this amount . And it's really handy to | |
00:20 | be able to work out fairly quickly what's , what | |
00:23 | this amount is with the least amount of hassle as | |
00:26 | possible , I guess with the least amount of bother | |
00:28 | . So this is going to be aimed at looking | |
00:30 | at this . So there's a couple of concepts . | |
00:32 | I'm going to be tying in together with this . | |
00:34 | Okay . I'm trying to by the , make the | |
00:38 | calculations as simple as possible . So Let's have a | |
00:42 | look at this . And so you went to a | |
00:44 | shop and something was , I started nice and easy | |
00:47 | . Something was $20 and we wanted to take off | |
00:51 | . Um What about we take off 20% . Now | |
00:57 | look , you could work out 20% of 20 and | |
00:59 | we could take that off . But there's a I | |
01:01 | think it's really before we go on , it's really | |
01:03 | important to get this idea what Taking off 20% is | |
01:06 | because $20 itself is $20 is the original amount . | |
01:09 | This is the 100% . 100% of the amount out | |
01:14 | of 100 . This is 100% . We're taking off | |
01:17 | 20% . So this is the same as 100% , | |
01:22 | taking 20% , working at 80% of the number . | |
01:26 | Okay , so straight away , when you said it's | |
01:28 | taken by 80% if you take this 20 off , | |
01:31 | 100 you won't realize that what you're actually working out | |
01:35 | is rather than , you know , and this is | |
01:38 | why the numbers are still simple . You're actually just | |
01:40 | working at 80% of this number here . Okay , | |
01:44 | this is Okay , so this is where we take | |
01:47 | 20% off . Okay . You good with that ? | |
01:49 | Yeah , this is gonna , so first off , | |
01:51 | that's a really big idea to get that . It's | |
01:53 | a great idea . It's not too hard . That's | |
01:54 | the first step . I recommend when we're doing the | |
01:57 | next step , would all recommend ? Is this a | |
01:59 | bit of a trick for working out percentages mentally ? | |
02:02 | We've explored these in other videos as well . And | |
02:05 | so this is as follows . So that's the idea | |
02:08 | of 100% 50% 10% 5% to work this out really | |
02:20 | quickly . And that's simple that they're very simple . | |
02:22 | Okay . And I'll show you how Um so it's | |
02:25 | 100% is the whole number , so say $20 here | |
02:28 | . 100% . He's 20 . 50% is half of | |
02:33 | 100 . Okay , so it's 1020 , which is | |
02:36 | 10 , we have 10% 100 divided by 10 . | |
02:43 | So 1/10 of that . So all we're doing is | |
02:45 | removing this this zero here . Okay . Or moving | |
02:49 | this decimal place , someone . So this becomes to | |
02:52 | 20 , divided by 10 is too And the same | |
02:55 | this uh 5% here , is this 50% divided by | |
02:59 | 10 or we're gonna move this decimal place . So | |
03:01 | this becomes one . So you got this idea ? | |
03:03 | That's pretty simple . Right ? So with 80 , | |
03:06 | we have a number of components that we could actually | |
03:08 | make up 80 by going 50 10 , 10 , | |
03:11 | 10 . Okay , at an early these together that's | |
03:14 | the same . We're going to go 10 plus two | |
03:16 | plus two plus two because this is the same as | |
03:18 | 80% . You get this idea , let's do it | |
03:22 | . So to work out this , we're going Um | |
03:26 | or even a simpler way , you might actually do | |
03:28 | this in your first starting to this you might work | |
03:30 | out 10% which is to And then there's 80% . | |
03:34 | It's nearly eight lots of that . Okay , so | |
03:37 | that's probably even a simpler way . We have 80 | |
03:40 | divided by , Sorry , 20 divided by 10 , | |
03:45 | Which is two times a day , which is 16 | |
03:49 | . Okay , So This is our answer . $16 | |
03:53 | . Now . This might have thrown you a little | |
03:55 | bit . So , we're gonna go through a few | |
03:57 | examples with this . All right there not too bad | |
03:59 | . Once you get a once you get the hang | |
04:01 | of them , so Let's give this another go . | |
04:08 | So , so we had to say something like again | |
04:10 | , we had a nice easy amount . Let's go | |
04:13 | $40 this time . And I want to take off | |
04:17 | uh at this time we take off 30 percent . | |
04:23 | Okay . They will get a bit nastier . Okay | |
04:26 | . So We're taking off 30% . But when you | |
04:28 | realize really , really quickly is taking off 30% is | |
04:31 | the same as working out how much 70% is 100 | |
04:34 | take away ? 30 or 70 . Yeah . So | |
04:36 | this is we just want to know what 70% of | |
04:39 | this number is . Okay , So the easiest way | |
04:42 | working at 70% is we can work out what seven | |
04:45 | lots of this 10% is . So 10% . Okay | |
04:49 | , 100% of 40 . It's 40 . And that | |
04:53 | divided by 10 is four and then seven fours we | |
04:57 | get our answer . Oh , 28 . Okay . | |
05:00 | So $28 . You good with this ? Okay . | |
05:07 | Because Again , is 40 . 10% is four , | |
05:13 | and then 70 is seven lots of 10 to 74 | |
05:16 | 28 . Okay . All right , let's work out | |
05:22 | another one of these and this , by the way | |
05:25 | , you don't need to have tattooed on your arm | |
05:27 | , anything like this , You can mentally think there's | |
05:29 | quite easily and trying to make them as simple as | |
05:32 | you can . I think when you're doing okay , | |
05:34 | obviously . So what about we did say something like | |
05:37 | and give this one to go before before I waffle | |
05:40 | on and finish it . What about we do say | |
05:42 | something of $50 and we wish to take off 25% | |
05:57 | . Okay , this is a bit harder this time | |
05:59 | . Yeah . Okay . So what we might work | |
06:01 | out with this is we might realize that if we | |
06:03 | first off , what what would you actually know is | |
06:06 | we want to know what 75 of 50 years ? | |
06:09 | Okay , So it's 75 percent of 15 , and | |
06:15 | this can be made up a couple of ways . | |
06:17 | Okay , We're gonna need Um seven of these tens | |
06:23 | and one of these fives . Okay . So First | |
06:28 | off , really quickly , what you might think is | |
06:29 | 10% of this is five and half of that's going | |
06:32 | to be $2.50 . Okay . Because it's gonna be | |
06:35 | the $5 listening to $2.50 bit , there's gonna be | |
06:38 | a five bits of 75 to 35 Plus $3 50 | |
06:44 | is 30 $7.50 . I can't . How did you | |
06:52 | go with that 1 ? All right . Now , | |
06:55 | look , I think it's that's probably the simplest way | |
06:58 | of doing these , but a lot of these , | |
06:59 | I know we can get into uh 10% . We | |
07:02 | get into more wonders than that . But a lot | |
07:03 | of sales that were talking more , it's these very | |
07:07 | uh 30% 25% of that sort of thing . Okay | |
07:11 | , I might give that 25% another . Okay ? | |
07:14 | In fact , no , let's go a step further | |
07:16 | than this . Let's get a different number and we'll | |
07:21 | go another one . Say what I wanted to do | |
07:24 | is I want to get this time 17 dollars . | |
07:30 | Let's go $72 , we can make it a little | |
07:33 | bit harder and I want to take off this time | |
07:37 | 75% . Now , this is a more difficult one | |
07:41 | . I think we all agree on this one . | |
07:42 | Right ? So first off this 75% , we're going | |
07:45 | to see that again as we're just working at 25% | |
07:50 | of this amount . Okay , so this is to | |
07:54 | lots of this and one lot of this . Okay | |
07:58 | , so What we're going to be doing is we're | |
08:00 | gonna be adding $7 , 20 And $3.60 . Can | |
08:06 | you see that straight away ? So 7 20 plus | |
08:09 | 7 20 is $14.40 plus $3.60 is $18 now . | |
08:20 | I just want to double check that one . Okay | |
08:22 | so let's write this one down . Um So we | |
08:26 | have 10% 10% this is $7.20 and This one is | |
08:31 | going to be 360 . So we get to lots | |
08:35 | of these which is 1440 Plus , this is 15 | |
08:40 | , Last three is $18 . Now look obviously the | |
08:43 | more complex the numbers , the more complex the calculation | |
08:46 | is going to be in your hand . They're gonna | |
08:47 | get harder . So then you might employ things like | |
08:50 | if they start to get really silly , maybe you | |
08:52 | would look at this and say I like alcohol , | |
08:53 | that's 70 just to save myself mentally what's going on | |
08:56 | and and then you'll be able to work it out | |
08:58 | A little bit easier . So maybe you look at | |
08:59 | this and had 70 and then you can go , | |
09:01 | well , this is gonna be the same as seven | |
09:03 | and seven and $3.50 and you'll get a fairly close | |
09:07 | answer . Okay ? So anyway , hopefully you are | |
09:10 | good with those and they're nice and simple . Okay | |
09:13 | . Any comments ? Any questions , please let me | |
09:15 | know . Okay , see you then . |
Summarizer
DESCRIPTION:
OVERVIEW:
Work out percentage discounts instantly! is a free educational video by tecmath.
This page not only allows students and teachers view Work out percentage discounts instantly! videos but also find engaging Sample Questions, Apps, Pins, Worksheets, Books related to the following topics.